Devices such as cardiac pacemakers have been developed over the past several years for implanting in the body to aid or support a body function. These devices require a source of energy which must also be suitable for implanting in the body. In the past, chemical batteries have been employed for this purpose. However, chemical batteries have limited life times and so are not suitable for most applications because of the necessity for surgical intervention every few years to replace the power source.
The commonly assigned application cross-referenced above discloses an improved power source for implanting in the body comprising a microwatt thermoelectric generator utilizing a thermopile and nuclear fuel heat source. The thermopile is comprised of semiconductor thermoelectric elements, such as P- and N-type bismuth telluride elements, stacked together in a parallel array and separated by thin polyimide films. The semiconductor thermoelectric elements are approximately 15 mils square and about 3/4 inch long with a stack or array including about 36 elements. The elements are connected together by shoes which are alloyed into the end faces of the elements. With this arrangement, the microwatt thermoelectric generator is capable of an electric power output of 300 to 400 microwatts at approximately 0.3 volts using a nuclear power source equivalent to approximately 50 milliwatts of thermal energy which is generally equivalent to 1/10 gram of a suitable form of plutonium.
The microwatt thermoelectric general construction disclosed in the commonly assigned application cross-referenced above is a highly advantageous one. However, because of design constraints including size, it is difficult to place a sufficient number of semiconductor elements in the thermopile array to obtain the desired power output. Furthermore, the thermopile is comprised of semiconductor materials which are inherently brittle and exhibit low strength compared to metals when subjected to tensile or shearing loads. Tensile and shear loading tends to break or crack the semiconductor elements and/or electrical connectors causing electrical discontinuity and failure. Accordingly, one of the features of the thermopile mount disclosed in the commonly assigned application cross-referenced above is the provision of a support harness to place the thermoelectric elements under compression even under loading conditions which would otherwise result in tension or shear stresses.